Internal combustion engines have traditionally employed some form of valve gear lash adjustment. Typically, lash adjustment is accomplished mechanically or hydraulically. Of the hydraulic type, the most prevelant is the barrel lifter which comprises a generally cup-shaped body slidably disposed in a bore provided therefore in the engine block to contact the engine driven cam, and a piston disposed within the body to transmit movement from the lifter to the pushrod.
It is particularly important in valve lifter construction that the surface operating against the cam be formed of a wear resistant material and that the lifter body rotate within the block to ensure uniform wear of its cam engaging surface.
Recently, roller cam followers have become more popular as a method of lowering valve train friction and thus increasing engine efficiency. Roller cam followers typically comprise a cylindrical body portion which supports a roller at one end thereof for rotation about an axis parallel to the axis of the cam. Provision, however, must be made to ensure against rotation of the follower body. Such rotation would cause misalignment of the cam and roller axes, resulting in scuffing therebetween, undue wear and shortened service life. The most prevelant prior art approach for preventing the rotation of follower bodies is the rigid keying thereof to the engine block. This approach, however, has shortcomings in that it requires that precise rotational alignment be maintained between the roller and cam axes, not only at the time of manufacture but during the life of the engine. No accomodation has been made for dimension and material variations found in all manufacturing processes, or for wear induced variations. Finally, prior art implementations of roller cam followers necessitate substantial modification or redesign of the engine block itself, which is extremely expensive.